1. Field of the Invention
The present invention relates to a light guiding plate, a surface emitting device using the light guiding plate, and a liquid crystal display device using the light guiding plate. In particular, the invention relates to a light guiding plate capable of efficiently directing light to a viewer, a surface emitting device using the light guiding plate, and a liquid crystal display device using the light guiding plate.
2. Description of the Related Art
Conventionally, a surface emitting device which illuminates a liquid crystal display panel, for example, a frontlight has been known as an illumination unit of a display device, such as a liquid crystal display device. In general, a conventional frontlight is mainly composed of a light source, and a light guiding plate from which light emitted from the light source exits toward a liquid crystal display panel.
FIG. 10 is a view illustrating the configuration of a liquid crystal display device having a conventional frontlight. The liquid crystal display device shown in FIG. 10 includes a liquid crystal display panel 4, a frontlight disposed on the liquid crystal display device 4, and a cover 5 disposed on a light guiding plate of the frontlight. The frontlight has a light guiding plate 1. The light guiding plate 1 has a flat shape, and has a pair of main surfaces opposite to each other and a pair of end surfaces opposite to each other. One (a main surface close to a viewer) of the pair of main surfaces is provided with a plurality of prisms 1a. A bar-shaped light guide 3 is disposed near one of the pair of end surfaces, and a light source 2 is disposed at one end portion of the bar-shaped light guide 3.
In the frontlight, light emitted from the light source 2 is incident on an end surface of the light guiding plate 1 to propagate through the inside of the light guiding plate 1. The light reflected from the prisms 1a in the light guiding plate 1 is directed to the liquid crystal display panel 4, then is reflected from the liquid crystal display panel 4, and then passes through the light guiding plate 1 and the cover 5 to be directed to a viewing side, as shown by an arrow in the figure.
However, in the light guiding plate 1 shown in FIG. 10, the light is reflected from the prisms 1a to be directed to the liquid crystal display panel 4. As such, if the light is reflected from the prisms 1a having a shape shown in FIG. 10, it is not avoidable that some of the light components leak from a main surface having the prisms 1a. Further, the light reflected from the liquid crystal display panel 4 passes through the light guiding plate 1 and then even passes through the cover 5. At this time, some of the light components having passed through the light guiding plate 1 are reflected from the cover not to be transmitted through the cover 5, as shown by the arrow in FIG. 10. Therefore, with the light guiding plate having the configuration shown in FIG. 10, it is not possible to efficiently direct light to the viewer.